In the past, chromophore-assisted light inactivation (CALI) was known as a method to analyze the function of a protein by spacio-temporally inactivating a functional site of a target protein and identifying the functional site of that protein or function thereof (refer to Japanese Patent Application Publication (tokukai) No. 2000-206116, and Japanese Patent Application Publication (tokuhyou) No. 2002-531810). These patent publications disclose that malachite green, rhodamine derivatives, and fluorescein derivatives, etc. can be used as the photosensitive agent in CALI. It is also known that fluorescein derivatives are more suitable than malachite green as a photosensitive agent to be used in CALI (refer to Proc. Nat. Acad. Sci. USA, Vol. 95, pp. 4293-4298, Apr. 1988 Biophysics). Then, it is known that, when using fluorescein as the photosensitive agent, singlet oxygen contributes to the functional destruction in the target site in the target protein (refer to Proteomics 2002, 2, 247-255).
Meanwhile, the production of singlet oxygen in a variety of fluorescein derivatives is described in Photochemistry and Photobiology, Vol. 37, No. 3, pp. 271-278, 1983.
As described in the publications above, malachite green and fluorescein were used in the past as photosensitive agents in order to spacio-temporally destroy biological functions dependent on irradiation with light. However, it was necessary either to use a large quantity of light irradiation or an extended irradiation time because the amount of active oxygen produced per unit light irradiation was small when using these substances. Consequently, when using conventional photosensitive agents, there was concern about photo-toxicity caused by the intense light irradiation itself, and biological function analysis research requiring high time resolution could not be conducted. For this reason, an analytical method was sought in which the spacio-temporal destruction of biological function could be achieved with shorter and weaker light irradiation.